Hydrous oxides of metals from Group IV of the periodic table such as titanium and zirconium are well known inorganic ion exchangers. The metal hydrous oxides are also frequently referred to as metal hydroxides. They exist as microcrystalline environments of fixed ions and as such are highly selective, i.e. certain hydrous metal oxides or hydroxides will only react with particular elements. In the art the metal oxide or hydroxide is incorporated into a macroporous resin carrier molecule, usually an organic polymer. Historically, the problem with metal hydroxides in the ion exchange process is that they have very low mechanical strength. Heat treatment has been suggested as a means for increasing their strength. However, treatment with heat causes the hydroxyl groups to undergo condensation, thereby lowering the ion exchange capacity of the metal. By providing a method wherein a large amount of hydrous metal oxide can be firmly supported on a carrier molecule, the mechanical strength of the hydrous metal oxide is improved.
Carriers such as alumina gel, silica gel, activated carbon and macroporous strong cation resin-1 (Dow MSC-1) have shown success in the past for providing a substrate upon which hydrous metal oxides have been utilized in ion exchange processes. Bonding has been taught as being optimum, however, only where the hydrous metal oxide and the carrier possess opposite zeta potentials, i.e., opposite polarities so as to attract one another. This has always been found to depend on the pH of the system.
Hydrous zirconium oxide is selective for sulfate (SO.sub.4.sup.=) and borate (BO.sub.2.sup.-) ions. When bound to one of the aforementioned cationic resins (particularly commercially produced MSC-1), regeneration has been extremely difficult due to the presence of a sulfite (SO.sub.3.sup.=) ion exchange function within MSC-1. These systems after having reacted with the solution in question, have always required regeneration by treatment with an aqueous slurry of magnesium hydroxide Mg(OH).sub.2, followed by a water rinse and then treatment with dilute hydrochloric acid (HCl) to convert the exchange function to a chloride. If the cation exchange function within the resin could be eliminated, the hydrous metal oxide could be regenerated with aqueous sodium hydroxide (NaOH) instead of the aqueous magnesium hydroxide Mg(OH).sub.2. This regeneration is simplified because the cation exchange site in the MSC-1 is eliminated. That cation site would otherwise pick-up Mg.sup.++ or Ca.sup.++ or other alkaline earth metals and form insoluble hydroxides on regeneration with NaOH, KOH, etc.
Therefore, since the sulfate (SO.sub.4.sup.=) and borate (BO.sub.2.sup.-) removal abilities of the ion exchange mechanism are due to the hydrous metal oxide phase present therein, a substrate with no cation exchange capabilities would simplify the regeneration process. It has now been found that activated charcoal is such a substrate. Its success appears to be due to its ionically inert characteristics and its extensive pore structure. Its large surface area appears to facilitate maximum ion exchange and to increase the precipitation of hydrous metal oxide therein, giving high loadings of the hydrous metal oxide. A secondary value in the use of activated carbon was disclosed in the literature which indicates that activated carbon in and of itself has exhibited the ability to absorb sulfate (SO.sub.4.sup.=) ion. Binding between the metal oxide and the activated charcoal will be possible at a less restricted pH range than that known in the prior art.